text: Classical coordination compounds feature metals bound to "lone pairs" of electrons residing on the main group atoms of ligands such as HO, NH, Cl, and CN.  In modern coordination compounds almost all organic and inorganic compounds can be used as ligands.  The "metal" usually is a metal from the groups 3–13, as well as the trans-lanthanides and trans-actinides, but from a certain perspective, all chemical compounds can be described as coordination complexes.
  The stereochemistry of coordination complexes can be quite rich, as hinted at by Werner's separation of two enantiomers of [[hexol|[Co((OH)Co(NH))]]], an early demonstration that chirality is not inherent to organic compounds.  A topical theme within this specialization is supramolecular coordination chemistry.
  * Examples: [Co(EDTA)], [[Cobalt(III) hexammine chloride|[Co(NH)]]], TiCl(THF).
  Coordination compounds show a rich diversity of structures, varying from tetrahedral for titanium (e.g., TiCl) to square planar for some nickel complexes to octahedral for coordination complexes of cobalt.  A range of transition metals can be found in biologically important compounds, such as iron in hemoglobin.
  * Examples: iron pentacarbonyl, titanium tetrachloride, cisplatin